Heparin is best known as an inhibitor of the blood coagulation system and is thus widely used as an anticoagulant but has a number of other biological activities (Jaques 1979). It is a heterogeneous mixture of related molecules that can be fractioned according to size or affinity for antithrombin (Andersson et al 1976). Such heparin fractions vary considerably in their anticoagulant activity (Andersson et al 1976), which is dependent on antithrombin binding.
Heparin has been used for treatment of patients with Plasmodium falciparum malaria (Mitchell 1974; Munir et al 1980; Smitskamp and Wolthius 1971), with ambiguous results. In studies of Rhesus monkeys infected with Plasmodium knowlesi, treatment with heparin has, according to some authors (Dennis and Conrad 1968), efficiently cured the monkeys, while others have found it to be inefficient (Howard and Collins 1972; Reid and Sucharit 1972). In vitro heparin has been shown to inhibit invasion and development of P. falciparum (Butcher et al 1988; Sivaraman and Chowdhuri 1983) and in one of these studies the 50% inhibitory dose of heparin and of heparin fractions with high or low affinity for antithrombin III were reported to be the same; 1 mg/ml (Butcher et al 1988).